diff --git a/app.js b/app.js
index eb6a1f6..cacbaa7 100644
--- a/app.js
+++ b/app.js
@@ -369,7 +369,15 @@ async function createChatRoom() {
 
 async function joinChatRoom(e) {
   e.preventDefault();
-  const topicStr = document.querySelector('#join-chat-room-topic').value;
+  const topicStr = document.querySelector('#join-chat-room-topic').value.trim();
+
+  // Validate the topic string
+  const isValidTopic = /^[0-9a-fA-F]{64}$/.test(topicStr);
+  if (!isValidTopic) {
+    alert('Invalid topic format. Please enter a 64-character hexadecimal string.');
+    return;
+  }
+
   const topicBuffer = b4a.from(topicStr, 'hex');
   addRoomToList(topicStr);
   await joinSwarm(topicBuffer);